The manipulation of chemical and/or biological materials in a laboratory environment is often quite labor-intensive. Recent trends in laboratory equipment design therefore point toward greater automation of many of these manipulation steps. Among other things, automation increases the throughput of the analyses executed by the equipment, reduces the costs of manual labor in the laboratory, increases the reliability of the analyses and protects laboratory workers from undesired contact with hazardous chemical and/or biological materials.
One example of an automated assembly suitable for use in a laboratory apparatus is set forth in U.S. Pat. No. 6,627,156, issued Sep. 30, 2003, to Goodale et al. Among other things, the '156 patent discloses a piercing station for piercing container caps or thick stoppers of a container, such as a test tube. The piercing station has a structural frame with two vertical guide rods. A carriage assembly is slidably mounted on the guide rods and is driven to move up and down along them. The carriage assembly carries a blade holder, which, in turn, holds a piercing blade assembly. The blade assembly includes a center blade and to cross blades interlock together, such that the blade assembly has a generally modified H-shaped cross-section for piercing a cap.
In operation, containers having caps that are to be pierced are sequentially shuttled beneath the piercing blade assembly. The piercing blade assembly is then driven through the respective cap to form an opening therein. The pierced container is then shuttled to a further position at which a sampling probe enters the opening and aspirates an amount of the sample material from the interior of the container.
An improvement to the foregoing apparatus to execute closed tube sampling has been implemented in an LxI® Model laboratory instrument manufactured by Beckman Coulter, Inc. In this implementation, the piercing blade and the sampling probe form a single, vertically movable sub-carriage assembly that is fixed to a single, horizontally movable carriage assembly. As a result, the piercing blade and sampling probe both share the same motions. The single carriage assembly is mounted for horizontal movement along a gantry and is driven by a horizontal drive.
In operation, the sample tubes are presented in a rack under the blade/probe hardware. The carriage assembly first translates downward to pierce the closed stopper with the blade. The carriage then retracts upward and shifts horizontally to position the sampling probe above the sample tube. A second downward motion allows the probe to enter the tube through the pierced opening in the cap and to aliquot the sample.
There are several inherent disadvantages when attempting to transfer the specific geometry of the piercing/sampling apparatus to other laboratory apparatus platforms. Many of these disadvantages arise from the fact that various dimensions in the apparatus must be chosen to prevent unwanted interference of the blade and sample probe with the tubes. For example, the motion of the rack must necessarily present the tubes sequentially along a motion path that is perpendicular to the horizontal motion of the single carriage assembly if the size of the rack is to be optimal and accommodate the maximum number of tubes per linear rack length. Further, the spacing between the blade and the probe must be greater than one half of the diameter of the sample tube in order to ensure sequential clearance of the blade and the probe from the sample tube during their respective operations. Such limitations are not inherent in the improved gantry assembly set forth below.